The present invention relates to a phonoangiographic spectral analyser apparatus and particularly to such an apparatus for clinical application in non-invasive procedure for the analysis and diagnosis of occluded arteries and the like.
Graphic diagnosis of vascular disorders has historically used invasive procedures such as angiography, or alternatively Dopplet ultrasound anaylsis for a noninvasive procedure.
Analysis of vascular disorder is often critical in the prevention and treatment of vascular diseases such as arterial stenosis, as well as other peripheral vascular deseases. Since early 1970, a non-invasive procedure has been developed by C. F. Dewey, Jr. and R. S. Lees which is identified by the name of phonoangiographic analysis, and the method has been shown to be a basically sound diagnostic procedure for occluded arteries and the like.
Medical diagnosis of the human body has for many years involved the analysis of the heart and interrelated chest sounds generally under the broad identifying name of auscultation. Before the stethoscope, the physician would directly listen to the heart sounds through the chest wall, by placing his ear against the chest wall. Even with the more modern invention of the electronic stethoscopes, various recording instrumentation and the like, such diagnosis remains essentially a qualitative method of diagnosis. Further, development both from the standpoint of the technical instrumentation for processing of the sounds, as well as better knowledge and understanding of sound generation and transmission within the human circulating system is needed for quantitative analysis.
For example, an evaluation of phonoangiography is set forth in an article titled "Evaluation of Carotid Stenosis by Phonoangiography" prepared and submitted by Lees, Dewey et al. in the Nov. 27, 1975 issue of the New England Journal of Medicine. The particular study discussed was directed to carotid stenosis and the author concluded that the method presented was a non-invasive method of bruit analysis which could be used to determine the extent of stenosis. In this procedure, a microphone is applied to an area above the artery. The turbulence associated with a stenosis in the artery produces a bruit (a noise) which is processed by the pick-up device into a spectral display. As noted in the above article, the frequency spectrum provided an appropriate basis for analysis and determination of the location and size of a stenosis. Generally, it has been recognized that the size of the internal diameter of the occluded artery is defined by the equation EQU f.sub.o d.sub.o =US=500
where,
U is the blood flow velocity--in millimeters (mm) per second, PA1 f.sub.o is the critical frequency of the spectrum in Hertz (Hz), PA1 d is the diameter of the arterial opening or passageway in mm, PA1 S is equal to 1 (Strouhal) number.
The constant number 500 to which the equation is set is based on estimated flow rate in the artery of 500 mm per second. Appropriate positive measurement experimentation has shown that the formula provides a highly accurate estimate of the occluded diameter of the artery. In particular, the results compare favorably with diagnostic findings based on other established methods such as the Dopper ultrasound method and the digital substractive angiographic method presently in use.
The theoretical work done today has shown a sound basis for use of the process in theory. Prior art work thus included development of and confirming of hemodynamic theories from which one can properly and quite accurately estimate the diameter of the opening in an occluded artery based on the acoustic frequency spectrum, as well as analysis of other diseases and respiration defects which are related to acoustic spectra. Generally, medical usage to date has been related to monitoring the internal carotid artery, but it is recognized that the technique may also be useful in analysing the aortic artery as well as other areas of arterial stenosis. The development of the prior art thus generally involves recording of the measurements and subsequent processing through a digital computer. This of course requires substantial investment and further does not provide an on-line presentation for real time analysis. The computer based instrumentation such as used to-date cannot therefore be considered as a usable concept for use in the small clinic or the doctor's office and the like because of space and cost.
Although the work done to date has clearly established the validity of the diagnostic method as well as the possibility of appropriate accuracy, a significant need remains for a practical clinical instrument. In order to provide a useful clinical instrument, the apparatus must be relatively inexpensive and reasonably portable while maintaining reliability at least equal to present analysis in other forms of instrumentation. Further, it is desirable for clinical analysis to provide a real time instrument with the display of the information in real time and essentially instantaneously with the monitoring of the condition.
In such systems, the measurement is of the audio frequency acoustical signal generated by the human artery as a result of a stenosis condition causing turbulence which is heard as a bruit. Thus, turbulent blood flow produces characteristic sound patterns which will vary in accordance with the size and shape of the occlusion.